1. Field of the Invention
The present invention relates to a combustion-type power tool, such as combustion-powered fastener-driving tool for driving fasteners, such as nails, into a workpiece.
2. Description of the Related Art
Combustion-type power tools have been known in the art as disclosed in Japanese Patent Publication (B2) Nos. HEI-1-34753, HEI-4-48589, HEI-3-25307, HEI-4-11337, and SHO-64-9149.
Unlike a compressed-air type power tool that uses compressed air as a driving source, the combustion-type power tool requires no compressor and is, therefore, much easier to transport to a construction site or the like. Further, the combustion-type power tool can be conveniently provided with an internal power source, such as a battery, so that the tool can be used in any environment without requiring a commercial power supply.
Generally, the combustion-type power tool is made up of metal components, such as a cylinder, rubber components, such as shielding member, and plastic components, such as a housing. When fastener driving operations are successively performed with a short interval, heat generated by combustion is partly dissipated when a fan performs scavenging such that the exhaust gas in the combustion chamber can be scavenged therefrom, and is partly absorbed by the metal components, particularly by the cylinder and a combustion chamber frame. The temperature of these metal components gradually increases and finally they become overheated. When the cylinder and the combustion chamber frame become high temperature, the gas remaining in the combustion chamber is not sufficiently cooled down so that thermal vacuum in the combustion chamber cannot be attained. Hence, delay occurs in returning the piston to the original position after the fastener driving operation is performed. Due to this delay, a cycle speed for completing one-shot fastener driving operation is lowered and so the work efficiency is degraded.
If the fastener driving operation is continued, the housing and the handle disposed near the combustion chamber frame and the cylinder are also heated up. The operator grasping the handle may not be able to continue the fastener driving operation. If so, the work efficiency is further degraded.
The sealing member, which is made from rubber and used for sealing the combustion chamber, may thermally be damaged and sealing capability with the sealing member may not be maintained. If it is the case, the combustion chamber is communicated with external atmosphere and the flammable gas introduced into the combustion chamber will not be ignited. Then, the fastener driving operation can no longer be continued even if the trigger switch is turned on. The housing, which is made from plastic, may also be damaged or distorted by the heat. If the sealing member and/or the housing is damaged, the tool needs to be disintegrated and a damaged component has to be replaced with a new one.